Jim made an interesting comment about the placement of zone 1 at 0.1 above film base plus fog in the "Victoms of the Zone System" thread by Chuck1. While I know this is the conventional wisdom with respect to the location of zone 1 (BTZS and ZS), I have had a similar finding to his. For the actual use of film, he states that zone III should be placed at closer to 0.4 above FB+ fog for any real use of shadow values.
I'd been trying to balance film with azo paper, on and off for a year and a half, and am finally having some success. One large problem has been the selection of film speed. I'd been beating my head against the rock, trying to figure out how claims for full film speeds and full shadow values could be made. After doing film tests which were useless for actual print making, I have come to the conclusion that tests should be done to give exposure which is far above the "normal" amount of light if shadow detail is to be of any real use in a print on azo.
I suspect my stubborn use of Efke 25 for azo has been a large part of my self-imposed frustration. I have finally settled on asa 6 as my "normal" film speed for grade 2 azo. Fortunately, Efke 25 is very long on contrast (up to 3.0 with some developers). If you look at the data on J&C's site, you can see a toe which goes well up towards 1.0 before it gets to the straight line portion of the film. Since I don't have a densitometer, I don't have actual numbers to go by. This finding for shadow values has been verified by in a similar manner (step wedge testing, FP4+) with different films and has shown a departure from the conventional wisdom as well.
I'm wondering if this is peculiar to azo and tests, or if others under rate film this much as a rule? What about alternative process, are there similar findings about exposure and shadow values? Thanks, tim